The invention relates to improvements in presses for pressing liquid from a traveling fibrous web, and more particularly to an improved extended nip press which extracts water from a traveling paper web.
In a conventional papermaking machine after the web is formed, it is carried through a press section where the water is mechanically expressed from the fibrous web. Improvements in press sections have included changes from the conventional two roll press to what is known as an extended nip press when the web is subjected to a continuing pressure for a longer period of time in each press nip than with a simple two roll press. Developments in these extended nip presses have included a roll as one of the pressing members with the other pressing member being a continuous impervious belt pressed toward the roll by an arcuate sliding shoe which develops a film of dynamic hydraulic fluid between the belt and shoe to eliminate friction and thus help aid in developing uniform pressure completely across the pressing zone through which the web presses. An example of such improved shoe press is shown in U.S. Pat. No. 3,783,097, E. J. Justus. In present high speed papermaking machines, the press must be capable of high nip pressures and of operating continuously and reliably over relatively long operating periods without the necessity of shutting down the operation. An important objective in any pressing operation is to obtain uniform extraction of water across the width of the nip. The uniform extraction is a direct function of the uniform pressure. In all paper machines, and particularly those of wide width, the bending caused by the application of forces must be compensated for so that forces in the center of the web are the same as at the edges.
It is accordingly an object of the present invention to provide an improved extended nip press which is capable of an improved pressing operation, and particularly is capable of producing uniform water extraction by the application of uniform pressure along the nip length.
A further object of the invention is to provide an improved extended nip press which is of a simplified construction so that manufacturing costs are reduced, so that the complexity of operating parts is minimized, and the structure is capable of continued high speed operation without wear of parts.
A further object of the invention is to provide an improved extended nip press capable of avoiding contamination to the web by the oil used in the parts being prevented from reaching the web because of the nature of the structure.